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#1
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Saddle position/setback on a new frame
I just need a mental double-check on something...
I bought a new (used) bike frame and both bikes are 73-degree seat tube angles. 2009 Fuji Team Carbon to a newer 2014 Trek Madone 4.9 I was fitted on the Fuji before, so does this mean I can take that same seatpost from the Fuji, drop it in the Madone at the proper seat height and everything will be the same? I feel like I know the answer is YES, but the Madone feels way further back over the rear wheel... |
#2
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Yes if they're the same angle.
You'd feel more over the rear wheel if the Fuji had longer chainstays and the Trek had shorter chainstays. You could probably feel that way if the Trek had a longer reach/lower stack too. |
#3
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I've already put a 0-setback post on the Madone based on "feeling", but that might have been unecessary... |
#4
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You should get accustomed to sticking the bike's rear wheel in a corner and measuring the X/Y position of the BB and the X/Y position of the front/top of the saddle. It allows you to adjust two bikes to fit exactly the same with quite a bit of precision.
You are looking to measure "Y" as the vertical distance from the center of the BB to the top of the saddle. X is the horizontal distance the saddle is behind the BB. It takes all the guesswork out of the old fashioned method of measuring up the seat tube. I think Lennard Zinn or someone has a webpage about it. But for two bikes with the same STA this should be really easy. |
#5
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If you go to a bike with a different STA, the vertical distance should remain the same. To make sure that it does, you can calculate the distance up the STA by putting the following in Excel =(vertical height from old bike) / COS(RADIANS(90-STA of new bike). If you only know the height along the STA from the old bike and want to know the vertical height, use =(height up the STA) x COS(RADIANS(90-STA)). |
#6
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You should have the your body positioned at the same position, relative to the BB. If I have two bikes with the same saddle, just drop a plumb bob from the saddle nose and measure how far back it is from the crank center line.
If something feels off after that, then it's the reach or drop that need changing. If you have your body too far forward, which will probably be the case with a zero setback post, you should feel too much weight on your hands. |
#7
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#8
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I do all of this (^, ^^, ^^^) with a drywall square held with the short end on the floor. Gives you an accurate saddle position behing BB center accounting for floor slope as well....
__________________
“A bicycle is not a sofa” -- Dario Pegoretti |
#9
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+1 for drywall square.
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#10
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Wavy concrete floors make for unreliable measurements with a drywall square. With a plumb bob, the floor doesn't have to be level or free of waviness, if the two bikes being compared are placed in the same spot for comparison.
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#11
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Yeah I did the plumbbob method when I originally set this bike up, but it never "felt" right. I'll get my measurements from my fitter and make sure to put the setback back to where it should be.
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#12
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Who says we're doing it on a wavy concrete floor? Geez...
__________________
“A bicycle is not a sofa” -- Dario Pegoretti |
#13
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the answer is yes
your saddle will be in the same spot relative to the BB, which is where you want to be for pedaling efficiency. now does this mean you may feel further forward or backward in relation to the front center? or front wheel? sure, the rear wheel may be further back or further forward on one bike. the fork on one bike may have more or less rake, putting the front wheel further from you, or closer to you, all of these things could make you feel like you are sitting further back on the madone. so maybe the madone has a rear wheel tucked in closer? or maybe the head tube is more slack? im kinda surprised theres that much difference |
#14
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I've never seen a concrete floor that wasn't wavy. They screed the concrete with a 2×4, then hand trowel the concrete to make a smooth surface, but it's never very flat.
Get a 6 foot level and place it on the floor. With feeler gauges, you'll probably find some significant ups and downs. Working in the machine shop business for many yeas gives me an appreciation for a flat surface. Building a house showed me how uneven most concrete floors really are. If you laid a 4x8 of 3/4" MDF on the floor, it would make a more suitable measuring surface. |
#15
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Quote:
__________________
“A bicycle is not a sofa” -- Dario Pegoretti Last edited by OtayBW; 12-11-2019 at 11:09 AM. |
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